1. Field of the Invention
The present invention relates to novel ceramic compositions based on boron nitride and to a process for the preparation thereof.
This invention also relates to novel composite ceramic materials, and articles shaped therefrom, comprising said boron nitride compositions.
2. Description of the Prior Art
Boron nitride is increasingly in demand in this art in light of its high thermal stability, its resistance to thermal shock, its great chemical inertness and its very good thermal conductivity. On the other hand, its low electrical conductivity makes it an insulator of choice.
Several processes are presently known to the art for the preparation of boron nitride.
One such process includes reacting boron trichloride with ammonia in the gaseous state. A fine boron nitride powder is obtained in this manner, which may be sintered to produce solid shaped articles.
More recently, it was discovered that boron nitride could be produced by the pyrolysis of precursor polymers.
The advantage of this "polymer" method primarily resides in the form of the final product, and, more particularly, enables the production, after pyrolysis, of boron nitride fibers.
The problem is that the boron nitride produced by one or the other of the above processes does not always have those properties which are adequate for certain specific applications.
Thus, more precisely, in the case of the manufacture of composite ceramic products based on boron nitride and silicon compounds, it is desirable to employ a boron nitride based material that is highly compatible with said silicon compounds, such as to enable the production of composites having improved properties.